German Preliminary Published Application DE 10 2013 001 095 A1 discloses a method for operating a hybrid drive system, whereby the hybrid drive system has an internal combustion engine that can be operatively connected to a first axle of the motor vehicle, a first electric motor that can likewise be operatively connected to the first axle as well as a second electric motor that can be operatively connected to a second axle of the motor vehicle. The electrical energy used to operate the second electric motor is generated by the first electric motor powered by the internal combustion engine in that the output of the internal combustion engine is increased, or else it is drawn exclusively from a storage device for electrical energy.
European patent specification EP 1 074 087 B1 discloses a method and an apparatus for controlling the internal combustion engine of an electric hybrid vehicle, whereby an electric motor or a motor/generator is installed between the engine and the continuously variable or automatic transmission, and whereby the hybrid vehicle has a battery and associated control elements. In this context, a control means essentially maintains the power output of the internal combustion engine along an ideal operating line as the speed of the engine varies. A second electric motor can also be provided and the torque output of the second electric motor can be varied by means of system controls.
German Preliminary Published Application DE 10 2012 103 292 A1 discloses a method for operating an electric drive train of a vehicle, whereby at least two electric motors, which are each operatively connected to a drive axle, as well as a control unit are provided, whereby the torque desired by the driver for the motor operation or the generator operation is determined, and whereby, at a given driven rotational speed, the requisite total power output of the electric driven train is determined, and whereby the power outputs of the individual electric motors are determined, and whereby the resulting power losses of the individual electric motors are minimized on the basis of stored power loss characteristic maps for the individual electric motors.
German Preliminary Published Application DE 10 2009 019 485 A1 discloses a drive train comprising a first electric motor and a planetary gear train as well as vehicles that have this drive train. The drive train has a first electric machine that can be operated in the motor or generator operating state, and a planetary gear train with a rotational speed changing device, whereby the planetary gear train has a drive side and a driven side, and whereby the first electric machine, when in its motor or generator operating state, interacts with the rotational speed changing device for control purposes so that a transmission ratio is established in the planetary gear train. The transmission ratio of the planetary gear train is influenced by the first electric machine, as a result of which the operating point of the internal combustion engine is also determined. The internal combustion engine is operated close to its optimal degree of efficiency. During a purely electric mode of operation, the second electric machine functions as a motor while the first electric machine is idling or is used as an additional drive. Part of the mechanical energy generated by the internal combustion engine is transformed into electrical energy by the first electric machine and transferred directly to the second electric machine. The second electric machine provides assistance for the accelerations. In the case of a deceleration, the energy storage unit can be charged by recuperating the braking energy.
The translation of European patent specification DE 602 23 850 T2 discloses a method for operating a drive system of a hybrid vehicle, whereby the hybrid vehicle comprises an internal combustion engine, a first electric motor/generator, a planetary gear mechanism and a second electric motor/generator. The ratio between a first torque that is generated by the internal combustion engine on the vehicle axles and a second torque that is generated by the second electric motor on the vehicle axles at each gear position of the transmission is changed from a first ratio, when the internal combustion engine as well as the second electric motor are operating normally, over to a second ratio, when either the internal combustion engine or the second electric motor is faulty.
German Preliminary Published Application DE 10 2007 054 368 A1 discloses a control architecture for the selection of an optimal mode or of an optimal gear and input speed for a hybrid powertrain system comprising an internal combustion engine, a first and a second electric motor and an electromechanical transmission system that is selectively operative in order to transmit torque between these and that is operative in a plurality of fixed gear modes and continuously variable modes. Preferred operating conditions and preferred costs are determined for each permissible operating range state and, on this basis, a preferred operating range state is selected. Cost-structure information that is entered into a strategic manager segment and used in an optimization segment preferably comprises operating costs which are generally determined on the basis of factors related to vehicle drivability, fuel economy, emissions and battery life for the determined torque range. Furthermore, costs are assigned to and associated with fuel and electrical power consumption associated with a specific operating point of the powertrain system for the vehicle. The optimum operating costs can be determined by calculating the total powertrain system loss, comprising a term based on engine power loss driven by fuel economy and exhaust emissions, plus losses in the mechanical system, losses in the electrical system and heat losses.
A hybrid vehicle known from the state of the art can be powered by various drive aggregates of the drive system. Powering the hybrid vehicle with one drive aggregate or the other can be advantageous, for example, in terms of energy consumption, but it can have detrimental consequences for the performance of the hybrid vehicle. Consequently, the state of the art faces difficulties when it comes to choosing which drive aggregate should be used to power the hybrid vehicle in a given driving situation.